/*-
 * Copyright (c) 1991, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      @(#)queue.h     8.5 (Berkeley) 8/20/94
 * $FreeBSD: stable/9/sys/sys/queue.h 252365 2013-06-29 04:25:40Z lstewart $
 */

#ifndef QUEUE_H
#define QUEUE_H

/* #include <sys/cdefs.h> */
#define __containerof(ptr, type, field) ((type *)((char *)(ptr) - ((char *)&((type *)0)->field)))

/*
 * This file defines four types of data structures: singly-linked lists,
 * singly-linked tail queues, lists and tail queues.
 *
 * A singly-linked list is headed by a single forward pointer. The elements
 * are singly linked for minimum space and pointer manipulation overhead at
 * the expense of O(n) removal for arbitrary elements. New elements can be
 * added to the list after an existing element or at the head of the list.
 * Elements being removed from the head of the list should use the explicit
 * macro for this purpose for optimum efficiency. A singly-linked list may
 * only be traversed in the forward direction.  Singly-linked lists are ideal
 * for applications with large datasets and few or no removals or for
 * implementing a LIFO queue.
 *
 * A singly-linked tail queue is headed by a pair of pointers, one to the
 * head of the list and the other to the tail of the list. The elements are
 * singly linked for minimum space and pointer manipulation overhead at the
 * expense of O(n) removal for arbitrary elements. New elements can be added
 * to the list after an existing element, at the head of the list, or at the
 * end of the list. Elements being removed from the head of the tail queue
 * should use the explicit macro for this purpose for optimum efficiency.
 * A singly-linked tail queue may only be traversed in the forward direction.
 * Singly-linked tail queues are ideal for applications with large datasets
 * and few or no removals or for implementing a FIFO queue.
 *
 * A list is headed by a single forward pointer (or an array of forward
 * pointers for a hash table header). The elements are doubly linked
 * so that an arbitrary element can be removed without a need to
 * traverse the list. New elements can be added to the list before
 * or after an existing element or at the head of the list. A list
 * may be traversed in either direction.
 *
 * A tail queue is headed by a pair of pointers, one to the head of the
 * list and the other to the tail of the list. The elements are doubly
 * linked so that an arbitrary element can be removed without a need to
 * traverse the list. New elements can be added to the list before or
 * after an existing element, at the head of the list, or at the end of
 * the list. A tail queue may be traversed in either direction.
 *
 * For details on the use of these macros, see the queue(3) manual page.
 *
 *                              SLIST   LIST    STAILQ  TAILQ
 * _HEAD                        +       +       +       +
 * _HEAD_INITIALIZER            +       +       +       +
 * _ENTRY                       +       +       +       +
 * _INIT                        +       +       +       +
 * _EMPTY                       +       +       +       +
 * _FIRST                       +       +       +       +
 * _NEXT                        +       +       +       +
 * _PREV                        -       +       -       +
 * _LAST                        -       -       +       +
 * _FOREACH                     +       +       +       +
 * _FOREACH_FROM                +       +       +       +
 * _FOREACH_SAFE                +       +       +       +
 * _FOREACH_FROM_SAFE           +       +       +       +
 * _FOREACH_REVERSE             -       -       -       +
 * _FOREACH_REVERSE_FROM        -       -       -       +
 * _FOREACH_REVERSE_SAFE        -       -       -       +
 * _FOREACH_REVERSE_FROM_SAFE   -       -       -       +
 * _INSERT_HEAD                 +       +       +       +
 * _INSERT_BEFORE               -       +       -       +
 * _INSERT_AFTER                +       +       +       +
 * _INSERT_TAIL                 -       -       +       +
 * _CONCAT                      -       -       +       +
 * _REMOVE_AFTER                +       -       +       -
 * _REMOVE_HEAD                 +       -       +       -
 * _REMOVE                      +       +       +       +
 * _SWAP                        +       +       +       +
 *
 */

/*
 * Singly-linked List declarations.
 */
#define SLIST_HEAD(name, type, qual)                                    \
    struct name {                                                       \
        struct type *qual slh_first; /* first element */                \
    }

#define SLIST_HEAD_INITIALIZER(head)                                    \
    { NULL }

#define SLIST_ENTRY(type, qual)                                         \
    struct {                                                            \
        struct type *qual sle_next;  /* next element */                 \
    }

/*
 * Singly-linked List functions.
 */
#define SLIST_INIT(head) do {                                           \
        SLIST_FIRST((head)) = NULL;                                     \
    } while (0)

#define SLIST_EMPTY(head) ((head)->slh_first == NULL)

#define SLIST_FIRST(head) ((head)->slh_first)

#define SLIST_NEXT(elm, field) ((elm)->field.sle_next)

#define SLIST_FOREACH(var, head, field)                                 \
    for ((var) = SLIST_FIRST((head));                                   \
         (var);                                                         \
         (var) = SLIST_NEXT((var), field))

#define SLIST_FOREACH_FROM(var, head, field)                            \
    for ((var) = ((var) ? (var) : SLIST_FIRST((head)));                 \
         (var);                                                         \
         (var) = SLIST_NEXT((var), field))

#define SLIST_FOREACH_SAFE(var, head, field, tvar)                      \
    for ((var) = SLIST_FIRST((head));                                   \
         (var) && ((tvar) = SLIST_NEXT((var), field), 1);               \
         (var) = (tvar))

#define SLIST_FOREACH_FROM_SAFE(var, head, field, tvar)                 \
    for ((var) = ((var) ? (var) : SLIST_FIRST((head)));                 \
         (var) && ((tvar) = SLIST_NEXT((var), field), 1);               \
         (var) = (tvar))

#define SLIST_INSERT_HEAD(head, elm, field) do {                        \
        SLIST_NEXT((elm), field) = SLIST_FIRST((head));                 \
        SLIST_FIRST((head)) = (elm);                                    \
    } while (0)

#define SLIST_INSERT_AFTER(slistelm, elm, field) do {                   \
        SLIST_NEXT((elm), field) = SLIST_NEXT((slistelm), field);       \
        SLIST_NEXT((slistelm), field) = (elm);                          \
    } while (0)

#define SLIST_REMOVE_AFTER(elm, field) do {                             \
        SLIST_NEXT(elm, field) =                                        \
            SLIST_NEXT(SLIST_NEXT(elm, field), field);                  \
    } while (0)

#define SLIST_REMOVE_HEAD(head, field) do {                             \
        SLIST_FIRST((head)) = SLIST_NEXT(SLIST_FIRST((head)), field);   \
    } while (0)

#define SLIST_REMOVE(head, elm, type, field) do {                       \
        if (SLIST_FIRST((head)) == (elm)) {                             \
            SLIST_REMOVE_HEAD((head), field);                           \
        }                                                               \
        else {                                                          \
            struct type *curelm = SLIST_FIRST((head));                  \
            while (SLIST_NEXT(curelm, field) != (elm))                  \
                curelm = SLIST_NEXT(curelm, field);                     \
            SLIST_REMOVE_AFTER(curelm, field);                          \
        }                                                               \
    } while (0)

#define SLIST_SWAP(head1, head2, type) do {                             \
        struct type *swap_first = SLIST_FIRST(head1);                   \
        SLIST_FIRST(head1) = SLIST_FIRST(head2);                        \
        SLIST_FIRST(head2) = swap_first;                                \
    } while (0)

/*
 * List declarations.
 */
#define LIST_HEAD(name, type, qual)                                     \
    struct name {                                                       \
        struct type *qual lh_first;  /* first element */                \
    }

#define LIST_HEAD_INITIALIZER(head)                                     \
    { NULL }

#define LIST_ENTRY(type, qual)                                          \
    struct {                                                            \
        struct type *qual le_next;   /* next element */                 \
        struct type *qual *le_prev;  /* address of previous next element */ \
    }

/*
 * List functions.
 */
#define LIST_INIT(head) do {                                            \
        LIST_FIRST((head)) = NULL;                                      \
    } while (0)

#define LIST_EMPTY(head) ((head)->lh_first == NULL)

#define LIST_FIRST(head) ((head)->lh_first)

#define LIST_NEXT(elm, field) ((elm)->field.le_next)

#define LIST_PREV(elm, head, type, field)                               \
    ((elm)->field.le_prev == &LIST_FIRST((head)) ? NULL :               \
     __containerof((elm)->field.le_prev, struct type, field.le_next))

#define LIST_FOREACH(var, head, field)                                  \
    for ((var) = LIST_FIRST((head));                                    \
         (var);                                                         \
         (var) = LIST_NEXT((var), field))

#define LIST_FOREACH_FROM(var, head, field)                             \
    for ((var) = ((var) ? (var) : LIST_FIRST((head)));                  \
         (var);                                                         \
         (var) = LIST_NEXT((var), field))

#define LIST_FOREACH_SAFE(var, head, field, tvar)                       \
    for ((var) = LIST_FIRST((head));                                    \
         (var) && ((tvar) = LIST_NEXT((var), field), 1);                \
         (var) = (tvar))

#define LIST_FOREACH_FROM_SAFE(var, head, field, tvar)                  \
    for ((var) = ((var) ? (var) : LIST_FIRST((head)));                  \
         (var) && ((tvar) = LIST_NEXT((var), field), 1);                \
         (var) = (tvar))

#define LIST_INSERT_HEAD(head, elm, field) do {                         \
        if ((LIST_NEXT((elm), field) = LIST_FIRST((head))) != NULL)     \
            LIST_FIRST((head))->field.le_prev = &LIST_NEXT((elm), field); \
        LIST_FIRST((head)) = (elm);                                     \
        (elm)->field.le_prev = &LIST_FIRST((head));                     \
    } while (0)

#define LIST_INSERT_BEFORE(listelm, elm, field) do {                    \
        (elm)->field.le_prev = (listelm)->field.le_prev;                \
        LIST_NEXT((elm), field) = (listelm);                            \
        *(listelm)->field.le_prev = (elm);                              \
        (listelm)->field.le_prev = &LIST_NEXT((elm), field);            \
    } while (0)

#define LIST_INSERT_AFTER(listelm, elm, field) do {                     \
        if ((LIST_NEXT((elm), field) = LIST_NEXT((listelm), field)) != NULL) \
            LIST_NEXT((listelm), field)->field.le_prev =                \
                &LIST_NEXT((elm), field);                               \
        LIST_NEXT((listelm), field) = (elm);                            \
        (elm)->field.le_prev = &LIST_NEXT((listelm), field);            \
    } while (0)

#define LIST_REMOVE(elm, field) do {                                    \
        if (LIST_NEXT((elm), field) != NULL)                            \
            LIST_NEXT((elm), field)->field.le_prev =                    \
                (elm)->field.le_prev;                                   \
        *(elm)->field.le_prev = LIST_NEXT((elm), field);                \
    } while (0)

#define LIST_SWAP(head1, head2, type, field) do {                       \
        struct type *swap_tmp = LIST_FIRST((head1));                    \
        LIST_FIRST((head1)) = LIST_FIRST((head2));                      \
        LIST_FIRST((head2)) = swap_tmp;                                 \
        if ((swap_tmp = LIST_FIRST((head1))) != NULL)                   \
            swap_tmp->field.le_prev = &LIST_FIRST((head1));             \
        if ((swap_tmp = LIST_FIRST((head2))) != NULL)                   \
            swap_tmp->field.le_prev = &LIST_FIRST((head2));             \
    } while (0)

/*
 * Singly-linked Tail queue declarations.
 */
#define STAILQ_HEAD(name, type, qual)                                   \
    struct name {                                                       \
        struct type *qual stqh_first;/* first element */                \
        struct type *qual *stqh_last;/* addr of last next element */    \
    }

#define STAILQ_HEAD_INITIALIZER(head)                                   \
    { NULL, &(head).stqh_first }

#define STAILQ_ENTRY(type, qual)                                        \
    struct {                                                            \
        struct type *qual stqe_next; /* next element */                 \
    }

/*
 * Singly-linked Tail queue functions.
 */
#define STAILQ_INIT(head) do {                                          \
        STAILQ_FIRST((head)) = NULL;                                    \
        (head)->stqh_last = &STAILQ_FIRST((head));                      \
    } while (0)

#define STAILQ_EMPTY(head) ((head)->stqh_first == NULL)

#define STAILQ_FIRST(head) ((head)->stqh_first)

#define STAILQ_NEXT(elm, field) ((elm)->field.stqe_next)

#define STAILQ_LAST(head, type, field)                                  \
    (STAILQ_EMPTY((head)) ? NULL :                                      \
     __containerof((head)->stqh_last, struct type, field.stqe_next))

#define STAILQ_FOREACH(var, head, field)                                \
    for((var) = STAILQ_FIRST((head));                                   \
        (var);                                                          \
        (var) = STAILQ_NEXT((var), field))

#define STAILQ_FOREACH_FROM(var, head, field)                           \
    for ((var) = ((var) ? (var) : STAILQ_FIRST((head)));                \
         (var);                                                         \
         (var) = STAILQ_NEXT((var), field))

#define STAILQ_FOREACH_SAFE(var, head, field, tvar)                     \
    for ((var) = STAILQ_FIRST((head));                                  \
         (var) && ((tvar) = STAILQ_NEXT((var), field), 1);              \
         (var) = (tvar))

#define STAILQ_FOREACH_FROM_SAFE(var, head, field, tvar)                \
    for ((var) = ((var) ? (var) : STAILQ_FIRST((head)));                \
         (var) && ((tvar) = STAILQ_NEXT((var), field), 1);              \
         (var) = (tvar))

#define STAILQ_INSERT_HEAD(head, elm, field) do {                       \
        if ((STAILQ_NEXT((elm), field) = STAILQ_FIRST((head))) == NULL) \
            (head)->stqh_last = &STAILQ_NEXT((elm), field);             \
        STAILQ_FIRST((head)) = (elm);                                   \
    } while (0)

#define STAILQ_INSERT_AFTER(head, tqelm, elm, field) do {               \
        if ((STAILQ_NEXT((elm), field) = STAILQ_NEXT((tqelm), field)) == NULL) \
            (head)->stqh_last = &STAILQ_NEXT((elm), field);             \
        STAILQ_NEXT((tqelm), field) = (elm);                            \
    } while (0)

#define STAILQ_INSERT_TAIL(head, elm, field) do {                       \
        STAILQ_NEXT((elm), field) = NULL;                               \
        *(head)->stqh_last = (elm);                                     \
        (head)->stqh_last = &STAILQ_NEXT((elm), field);                 \
    } while (0)

#define STAILQ_CONCAT(head1, head2) do {                                \
        if (!STAILQ_EMPTY((head2))) {                                   \
            *(head1)->stqh_last = (head2)->stqh_first;                  \
            (head1)->stqh_last = (head2)->stqh_last;                    \
            STAILQ_INIT((head2));                                       \
        }                                                               \
    } while (0)

#define STAILQ_REMOVE_AFTER(head, elm, field) do {                      \
        if ((STAILQ_NEXT(elm, field) =                                  \
             STAILQ_NEXT(STAILQ_NEXT(elm, field), field)) == NULL)      \
            (head)->stqh_last = &STAILQ_NEXT((elm), field);             \
    } while (0)

#define STAILQ_REMOVE_HEAD(head, field) do {                            \
        if ((STAILQ_FIRST((head)) =                                     \
             STAILQ_NEXT(STAILQ_FIRST((head)), field)) == NULL)         \
            (head)->stqh_last = &STAILQ_FIRST((head));                  \
    } while (0)

#define STAILQ_REMOVE(head, elm, type, field) do {                      \
        if (STAILQ_FIRST((head)) == (elm)) {                            \
            STAILQ_REMOVE_HEAD((head), field);                          \
        }                                                               \
        else {                                                          \
            struct type *curelm = STAILQ_FIRST((head));                 \
            while (STAILQ_NEXT(curelm, field) != (elm))                 \
                curelm = STAILQ_NEXT(curelm, field);                    \
            STAILQ_REMOVE_AFTER(head, curelm, field);                   \
        }                                                               \
    } while (0)

#define STAILQ_SWAP(head1, head2, type) do {                            \
        struct type *swap_first = STAILQ_FIRST(head1);                  \
        struct type **swap_last = (head1)->stqh_last;                   \
        STAILQ_FIRST(head1) = STAILQ_FIRST(head2);                      \
        (head1)->stqh_last = (head2)->stqh_last;                        \
        STAILQ_FIRST(head2) = swap_first;                               \
        (head2)->stqh_last = swap_last;                                 \
        if (STAILQ_EMPTY(head1))                                        \
            (head1)->stqh_last = &STAILQ_FIRST(head1);                  \
        if (STAILQ_EMPTY(head2))                                        \
            (head2)->stqh_last = &STAILQ_FIRST(head2);                  \
    } while (0)

/*
 * Tail queue declarations.
 */
#define TAILQ_HEAD(name, type, qual)                                    \
    struct name {                                                       \
        struct type *qual tqh_first; /* first element */                \
        struct type *qual *tqh_last; /* addr of last next element */    \
}

#define TAILQ_HEAD_INITIALIZER(head)                                    \
    { NULL, &(head).tqh_first }

#define TAILQ_ENTRY(type, qual)                                         \
    struct {                                                            \
        struct type *qual tqe_next;  /* next element */                 \
        struct type *qual *tqe_prev; /* address of previous next element */ \
    }

/*
 * Tail queue functions.
 */
#define TAILQ_INIT(head) do {                                           \
        TAILQ_FIRST((head)) = NULL;                                     \
        (head)->tqh_last = &TAILQ_FIRST((head));                        \
    } while (0)

#define TAILQ_EMPTY(head) ((head)->tqh_first == NULL)

#define TAILQ_FIRST(head) ((head)->tqh_first)

#define TAILQ_NEXT(elm, field) ((elm)->field.tqe_next)

#define TAILQ_PREV(elm, headname, field)                                \
        (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))

#define TAILQ_LAST(head, headname)                                      \
    (*(((struct headname *)((head)->tqh_last))->tqh_last))

#define TAILQ_FOREACH(var, head, field)                                 \
    for ((var) = TAILQ_FIRST((head));                                   \
         (var);                                                         \
         (var) = TAILQ_NEXT((var), field))

#define TAILQ_FOREACH_FROM(var, head, field)                            \
    for ((var) = ((var) ? (var) : TAILQ_FIRST((head)));                 \
         (var);                                                         \
         (var) = TAILQ_NEXT((var), field))

#define TAILQ_FOREACH_SAFE(var, head, field, tvar)                      \
    for ((var) = TAILQ_FIRST((head));                                   \
         (var) && ((tvar) = TAILQ_NEXT((var), field), 1);               \
         (var) = (tvar))

#define TAILQ_FOREACH_FROM_SAFE(var, head, field, tvar)                 \
    for ((var) = ((var) ? (var) : TAILQ_FIRST((head)));                 \
         (var) && ((tvar) = TAILQ_NEXT((var), field), 1);               \
         (var) = (tvar))

#define TAILQ_FOREACH_REVERSE(var, head, headname, field)               \
    for ((var) = TAILQ_LAST((head), headname);                          \
         (var);                                                         \
         (var) = TAILQ_PREV((var), headname, field))

#define TAILQ_FOREACH_REVERSE_FROM(var, head, headname, field)          \
    for ((var) = ((var) ? (var) : TAILQ_LAST((head), headname));        \
         (var);                                                         \
         (var) = TAILQ_PREV((var), headname, field))

#define TAILQ_FOREACH_REVERSE_SAFE(var, head, headname, field, tvar)    \
    for ((var) = TAILQ_LAST((head), headname);                          \
         (var) && ((tvar) = TAILQ_PREV((var), headname, field), 1);     \
         (var) = (tvar))

#define TAILQ_FOREACH_REVERSE_FROM_SAFE(var, head, headname, field, tvar) \
    for ((var) = ((var) ? (var) : TAILQ_LAST((head), headname));        \
         (var) && ((tvar) = TAILQ_PREV((var), headname, field), 1);     \
         (var) = (tvar))

#define TAILQ_INSERT_HEAD(head, elm, field) do {                        \
        if ((TAILQ_NEXT((elm), field) = TAILQ_FIRST((head))) != NULL)   \
            TAILQ_FIRST((head))->field.tqe_prev =                       \
                &TAILQ_NEXT((elm), field);                              \
        else                                                            \
            (head)->tqh_last = &TAILQ_NEXT((elm), field);               \
        TAILQ_FIRST((head)) = (elm);                                    \
        (elm)->field.tqe_prev = &TAILQ_FIRST((head));                   \
    } while (0)

#define TAILQ_INSERT_BEFORE(listelm, elm, field) do {                   \
        (elm)->field.tqe_prev = (listelm)->field.tqe_prev;              \
        TAILQ_NEXT((elm), field) = (listelm);                           \
        *(listelm)->field.tqe_prev = (elm);                             \
        (listelm)->field.tqe_prev = &TAILQ_NEXT((elm), field);          \
    } while (0)

#define TAILQ_INSERT_AFTER(head, listelm, elm, field) do {              \
        if ((TAILQ_NEXT((elm), field) = TAILQ_NEXT((listelm), field)) != NULL) \
            TAILQ_NEXT((elm), field)->field.tqe_prev =                  \
                &TAILQ_NEXT((elm), field);                              \
        else                                                            \
            (head)->tqh_last = &TAILQ_NEXT((elm), field);               \
        TAILQ_NEXT((listelm), field) = (elm);                           \
        (elm)->field.tqe_prev = &TAILQ_NEXT((listelm), field);          \
    } while (0)

#define TAILQ_INSERT_TAIL(head, elm, field) do {                        \
        TAILQ_NEXT((elm), field) = NULL;                                \
        (elm)->field.tqe_prev = (head)->tqh_last;                       \
        *(head)->tqh_last = (elm);                                      \
        (head)->tqh_last = &TAILQ_NEXT((elm), field);                   \
    } while (0)

#define TAILQ_CONCAT(head1, head2, field) do {                          \
        if (!TAILQ_EMPTY(head2)) {                                      \
            *(head1)->tqh_last = (head2)->tqh_first;                    \
            (head2)->tqh_first->field.tqe_prev = (head1)->tqh_last;     \
            (head1)->tqh_last = (head2)->tqh_last;                      \
            TAILQ_INIT((head2));                                        \
        }                                                               \
    } while (0)

#define TAILQ_REMOVE(head, elm, field) do {                             \
        if ((TAILQ_NEXT((elm), field)) != NULL)                         \
            TAILQ_NEXT((elm), field)->field.tqe_prev =                  \
                (elm)->field.tqe_prev;                                  \
        else                                                            \
            (head)->tqh_last = (elm)->field.tqe_prev;                   \
        *(elm)->field.tqe_prev = TAILQ_NEXT((elm), field);              \
    } while (0)

#define TAILQ_SWAP(head1, head2, type, field) do {                      \
        struct type *swap_first = (head1)->tqh_first;                   \
        struct type **swap_last = (head1)->tqh_last;                    \
        (head1)->tqh_first = (head2)->tqh_first;                        \
        (head1)->tqh_last = (head2)->tqh_last;                          \
        (head2)->tqh_first = swap_first;                                \
        (head2)->tqh_last = swap_last;                                  \
        if ((swap_first = (head1)->tqh_first) != NULL)                  \
            swap_first->field.tqe_prev = &(head1)->tqh_first;           \
        else                                                            \
            (head1)->tqh_last = &(head1)->tqh_first;                    \
        if ((swap_first = (head2)->tqh_first) != NULL)                  \
            swap_first->field.tqe_prev = &(head2)->tqh_first;           \
        else                                                            \
            (head2)->tqh_last = &(head2)->tqh_first;                    \
    } while (0)

#endif
